NMR Flashcards
What do the peaks show in NMR
Different external magnetic fields
Needed to bring to resonance
At a particular radio frequency
What compound produces a peak at 0
Tetramethylsilane
Draw TMS
See notes
Why is TMS used
⭕️ inert
⭕️ 12 H chemically equivalent - strong peak and single peak
⭕️ Peak to extreme right - outside normal range for most compounds
What unit is chemical shift measured in
Parts per million
Ppm
If something is to the left of TMS what term is used to describe it
Downfield
Further left = more downfield
How does an -OH affect chemical shift
- Electronegative O draws e towards it
- electron density around H decreases
- reduction in shielding
- the further away a H is ➡️ shielded to greater extent ➡️ need higher applied field to bring to resonance ➡️ further downfield
How big will a poorly shielded H’s chemical shift be
Large
How big will a highly shielded H’s chemical shift be
Small
What do different peaks represent in low resolution NMR
Different environments for H atoms
What does the ratio of areas under the peaks give an indication of
Ratio of number of H atoms in each environment
What does the integrator trace give a measure of
The relative area under peak
What is the definition of low resolution NMR
Spectrum which does not show the spin spin splitting pattern
What is the definition of high resolution NMR
Spectrum which does show the spin-spin splitting pattern
What is the definition of a doublet
Signal which appears as a pair of lines of equal intensity
What is the definition of a triplet
Signal which appears as three lines in the approximate intensity ratio 1:2:1
What is the definition of a quartet
A signal which appears as four lines in the approximate intensity 1:3:3:1
Describe the n+1 rule
The number of sub peaks is one more than the number of H attached to the next door carbon(s)
What are equivalent hydrogen atoms
H atoms attached to the same C atom
No splitting
Produce one peak
What happens when a H becomes deshielded
H bonded to O or N
Becomes more positive
What conditions can cause chemical shift to vary
Temperature
Solvent
Concentration
